For portable electronic products, alkaline and lithium batteries are generally used as the power sources. However, the battery has a tendency of gradually decreased voltage as the use time increases. To retain a stable output voltage, a two-stage power converter is typically employed, by which the input voltage supplied by the battery or batteries is stepped up first and then stepped down to the desired level.
FIG. 1 shows a conventional two-stage power converter 10, which comprises a boost converter 12 cascaded with a buck converter 14. Generally, the battery voltage Vbat is provided by two alkaline batteries or one lithium battery. The battery voltage Vbat is converted by the boost converter 12 to generate a first output voltage Vout1, and then the first output voltage Vout1 is converted by the buck converter 14 to generate a second output voltage Vout2. Unfortunately, the boost converter 12 and the buck converter 14 each has the conversion efficiency of about 90%, and therefore, the total efficiency of the two-stage power conversion is only about 81% or less. Namely, the overall efficiency of the two-stage power converter is reduced due to the cascaded conversion.
Therefore, it is desired a high efficiency power converter.